Method of manufacture of an anode composition for use in a rechargeable electrochemical cell

ABSTRACT

The invention described herein is directed to a method of manufacturing an anode composition for use in an electrochemical cell, in which the anode comprises an electrochemically active material, the method comprising the steps of mixing the electrochemically active material with an alkaline electrolyte solution, an organic surfactant, an indium compound, and a gelling agent, such that the indium compound or a portion thereof is added in an alkaline environment.

FIELD OF THE INVENTION

This invention relates to a method of manufacturing an anode compositionfor use in a sealed rechargeable cell.

BACKGROUND OF THE INVENTION

Rechargeable galvanic cells comprise a cathode, a zinc anode, aseparator having at least one layer of a semi permeable membrane and anaqueous alkaline electrolyte, such as an aqueous solution of potassiumhydroxide. The cathode may comprise manganese dioxide, hydrogenrecombination catalysts, hydrogen absorbers, or an air electrode.Graphite and/or carbon black is admixed to the cathode materials toprovide electronic conductivity and alkaline electrolyte is admixed toprovide ionic conductivity. The zinc anode mixture will include zinc ora zinc alloy as one of the main constituents, and will also includeelectrolyte and other constituents in known manner. These cells displaysuperior electrical performance, in particular at high discharge ratesand at low temperatures, and are widely used in many applications.

In contrast to rechargeable galvanic cells, primary galvanic cells areonly discharged once and then discarded. Therefore, the performancerequirements or expectations of primary and rechargeable cells arefundamentally distinct. Primary cells are expected to exhibit lowself-discharge rates and satisfy demanding performance requirements.Rechargeable cells, on the other hand, are expected to demonstrate goodcycle life and cumulative performance. Both types are expected to showlow rates of gassing, however, the mechanisms affecting gassing are verydifferent in rechargeable cells as gassing is measured over manyrecharge cycles, which alters the states of the electrodes many times.The recharge process of zinc electrodes is particularly troublesome dueto zinc redistribution and the high solubility of the zinc electrodedischarge product in strong alkaline electrolytes. These factorscontribute to or cause observed shape changes, poorer cycle life,gassing and formation of dendrites. As a result, it has been verydifficult to produce sealed rechargeable cells with zinc electrodeswithout providing a resealable venting mechanism that would releaseexcessive gassing during cycling and storage. It would be, therefore,not feasible to attempt to predict the effect of a change in, forexample, electrode make-up, on the performance of a rechargeable cellfrom the effect of such a change on the performance of primary cells.

Because of environmental concerns regarding disposal of batteries, toxicadditives in manganese/zinc cells such as mercury and lead are beingdrastically reduced or eliminated from the cells. U.S. Pat. No.5,626,988 describes in its background how the addition of mercuryprovides inhibition of zinc corrosion, resultant hydrogen gassing andelectrolyte leakage. It also describes how mercury provides conductivityin the anode resulting in superior electrical performance, in particularat high discharge rates, at low temperature and under conditions wherethe cells are exposed to mechanical shock and vibration. It furtherdescribes the use of surfactants and various metals including indium,for inhibiting corrosion and preventing dendrite formation inrechargeable cells.

Also described is known art relating to primary or single use galvaniccells regarding the problem of the surface coating of zinc powders withappropriate metals or their compounds, prior to processing the negativeelectrode, many of the techniques being complicated and frequentlyrequiring washing and drying steps.

U.S. Pat. No. 5,626,988 further describes a sealed rechargeable cellcontaining a mercury-free zinc anode and a method of manufacture, whichincludes treating a zinc or zinc alloy powder with indium sulfate, andmore particularly with both an organic surfactant and electrolyte. Thezinc powder is coated with a surfactant, and separately with an acidicaqueous solution of indium sulfate. Without any subsequent filtering,washing or drying, the powder is mixed with electrolyte and gellingagent and assembled into the cell.

SUMMARY OF THE INVENTION

In one broad aspect of this invention is a method of manufacturing ananode composition for use in a rechargeable electrochemical cell,wherein the anode comprises an electrochemically active material, themethod comprising the steps of:

-   -   (a) mixing said material with a first portion of an alkaline        electrolyte solution;    -   (b) mixing said material with an organic surfactant;    -   (c) mixing said material with a first indium compound;    -   (d) mixing to said material a second portion of said electrolyte        and a gelling agent.

In another broad aspect of this invention is a method of manufacturingan anode composition for use in a rechargeable electrochemical cell,wherein the anode comprises an electrochemically active material, themethod comprising the steps of:

-   -   (a) mixing said material with an organic surfactant;    -   (b) mixing said material with a first indium compound;    -   (c) mixing said material with a first portion of an alkaline        electrolyte solution;    -   (d) mixing said material with a second indium compound; and    -   (e) mixing to said material a second portion of said electrolyte        and a gelling agent.

This invention also contemplates a rechargeable cell comprising an anodehaving the composition manufactured in accordance with the methoddescribed herein; a cathode, an electrolyte; and a separator between theanode and the cathode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional elevation of a typical cylindrical cell asknown in the prior art.

FIG. 2 is an enlarged cross-sectional view of the bottom portion of thecell as shown in FIG. 2 of earlier U.S. Pat. No. 6,099,987.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a typical alkaline manganese dioxide-zincrechargeable cell comprises the following main units: a steel can 12,optionally coated with a conductive coating on the inside of the can,defining a cylindrical inner space, a manganese dioxide cathode 14formed by a plurality of hollow cylindrical pellets 16 pressed in thecan, a zinc anode 18 made of an anode gel and arranged in the hollowinterior of the cathode 14, and a cylindrical separator 20 separatingthe anode 18 from the cathode 14. The ionic conductivity between theanode and the cathode is provided by the presence of potassiumhydroxide, KOH, electrolyte added into the cell in a predeterminedquantity.

The can 12 is closed at the bottom, and it has a central circular pip 22serving as the positive terminal. The upper end of the can 12 ishermetically sealed by a cell closure assembly which comprises anegative cap 24 formed by a thin metal sheet, a current collector nail26 attached to the negative cap 24 and penetrating deeply into the anodegel to provide electrical contact with the anode, and a plastic top 28electrically insulating the negative cap 24 from the can 12 andseparating gas spaces formed beyond the cathode and anode structures,respectively.

The material of separator 20 consists of two different materials, i.e.:a first material made of fibrous sheet material wettable by theelectrolyte, and a second material being impermeable to small particlesbut retaining ionic permeability. An expedient material for the firstlayer is a sheet material of non-woven polyamide fiber, which isabsorbent and serves as a reservoir for electrolyte. The macro-porousstructure of the absorbent layer cannot prevent internal shorting byzinc dendrites or deposits during discharge/charge cycling.

Shorting is prevented by the second material, which may be a layer orlayers of micro-porous or non-porous material laminated to or coatedonto the fibrous sheet material. One suitable material is one or morecellophane membranes laminated to the non-woven polyamide sheet. Anotheris one or more coatings of regenerated cellulose or viscose coated ontoand partially impregnating the non-woven polyamide sheet, resulting in acomposite material.

One or more layers of the laminated or composite material are wound toform a cylindrical tube and placed into the hollow cylindrical cathodestructure.

As illustrated in FIG. 1, one prior art method of achieving sealing ofthe separator bottom is by means of a hot-melt bead 34, which was usedto seal the separator 20 to a washer 33 in the cell. In anothervariation the washer is omitted and hot-melt adhesive only is used.

FIG. 2 illustrates a bottom sealing means according to an earlierinvention described in U.S. Pat. No. 6,099,987. As shown, the sealing ofthe bottom of the separator 20 is achieved in that invention by two cups35 and 36, placed around and inside the bottom of the separator. Asmentioned above, the separator 20 is preferably comprised of two layers,shown as 20 a and 20 b. The cup or cups, 35 and 36, are made of amaterial comprising one or more thin micro-porous or non-porousmembranes laminated or coated onto one or more sheets of non-wovenfibrous porous sheet material. During placement, the non-woven fibrousmaterials of the separator and the cup or cups are compressed in theoverlap area 34 where the cup and/or cups overlap the bottom of theseparator 20. Any gaps between the separator and cup or cups formed bythe wrinkling of the thin micro-porous or non-porous layers are filledby the compressed fibers of the porous non-woven layers resulting in aneffective barrier to internal short circuits. This is accomplished byselection of the material in the cups and the shape and dimensions ofthe tools used to make the placement of the cups and the separator intothe hollow cathode cylinder.

In accordance with the present invention, the anode comprises of zinc asthe electrochemically active material. The zinc may be a mercury-free ormercury-free and lead-free zinc or zinc alloy. The mercury-free ormercury-free and lead-free zinc or zinc-alloy may be metallic, a powder,granular, particulate, or in the form of flakes but are not limited tothese forms. The metallic zinc powder preferably has a purity of 99.98%,while the zinc alloy powder preferably comprises 99% zinc. Up to about20% by weight of solid zinc oxide may be incorporated into the activematerial of the anode. The zinc alloy may comprise of mercury-free andlead-free zinc-bismuth alloy, mercury-free and lead-free zinc-bismuthalloy of finer particle size, zinc-lead alloy,zinc-aluminum-bismuth-indium alloy, zinc-calcium-bismuth-indium alloy,zinc-magnesium-bismuth alloy, and any combination thereof. The zinc maycontain up to 800 ppm lead, up to 800 ppm indium, up to 500 ppm calcium,up to 500 ppm magnesium, up to 200 ppm bismuth and up to 200 ppmaluminum.

In a first broad aspect of the invention, the electrochemically activematerial comprises a mercury-free or mercury-free and lead-free zinc orzinc alloy, which is first mixed with a first portion of an alkalineelectrolyte. The electrolyte is preferably potassium hydroxide, thefirst portion of which is usually added to about 40% of the totalelectrolyte volume. This ratio is, however, not critical as a 100% ofthe electrolyte can be applied in the first step, providing the blendingsystem or equipment can produce a lump free pumpable anode gel. It hasbeen determined however, that a preferable range for the first portionof the electrolyte is between about 20% to about 60% of the total volumeof electrolyte with about 40% being the most preferable. The zinc isthen mixed with an organic surfactant or wetting agent. A wetting agentor surfactant is effective in minute concentrations and should be stablein the alkaline electrolyte. The preferred surfactants for rechargeablecells are selected from the group of nonionic and ionic surfactantshaving a molecular weight of from about 300 to about 1500, and moreparticularly are compounds containing polyethylene oxide orpolypropylene oxide groups, their copolymers or any combination thereof.Particularly suitable surfactants include polyoxypropylene compounds,polyoxythelene compounds, their copolymers or any combination thereof.The materials are thoroughly mixed to assure complete mixing of the zincif surfactant is added at this stage. The zinc is then thoroughly mixedwith a first indium compound. The indium compound is preferably indiumsulfate either in the form of a solution or powder. The indium compoundcan also be indium oxide, indium hydroxide or indium acetate. The indiumcompounds used can be either in the form of a solution or a powder. Thisstep is then followed by the addition and thorough mixing of theremainder of the alkaline electrolyte and a gelling agent. This laststep can include the addition of nucleation additives such as magnesiumoxide, magnesium hydroxide, calcium oxide, calcium hydroxide, zirconiumoxide and any combination thereof The nucleation additives can also beadded directly to the electrochemically active material before any ofthe steps described herein.

Nucleation additives function as precipitation aids for zinc oxideduring discharge and zinc during the charging process. This results in abetter morphology of the rechargeable zinc anode, which can improveperformance and lower gassing.

The steps described above need not be carried out strictly in thesequential order described above. Some of the steps can be carried outsimultaneously with the proviso that the indium compounds are added inan alkaline environment and lead to an anode composition which providesfor a better performance rechargeable cell.

Thus, in another aspect, the addition of the organic surfactant canprecede the addition of the first portion of the alkaline electrolyte.

In another aspect, the addition of organic surfactant can precede theaddition of the first portion of the alkaline electrolyte and theaddition of the first indium compound is then followed by the additionof a second indium compound. If the first indium compound is indiumsulfate, the second indium compound can be indium sulfate, indium oxide,indium hydroxide, or indium acetate. The first and second indiumcompound can be in the form of a solution or in the form of a powder ora combination thereof.

In another aspect, the organic surfactant and the first indium compoundcan be added simultaneously.

In another aspect, the addition of the organic surfactant can precedethe addition of the first portion of the alkaline electrolyte and theaddition of the alkaline electrolyte and first indium compound can beadded simultaneously.

In another aspect, the addition of the first and second indium compoundcan be performed simultaneously. Alternatively, the first and secondindium compounds can be added simultaneously with the organicsurfactant.

In a second broad aspect of the invention, the electrochemically activematerial comprises a mercury-free or mercury-free and lead-free zinc orzinc alloy, which is first mixed with an organic surfactant or wettingagent. The preferred surfactants for rechargeable cells are selectedfrom the group of nonionic and ionic surfactants having a molecularweight of from about 300 to about 1500, and more particularly arecompounds containing polyethylene oxide or polypropylene oxide groups,their copolymers or any combination thereof. Particularly suitablesurfactants include polyoxypropylene compounds, polyoxythelenecompounds, their copolymers or any combination thereof. This step isfollowed by the addition of a first indium compound. The first indiumcompound may comprise indium sulfate, indium oxide, indium hydroxide orindium acetate and can be either in the form of a solution or a powder.The electrochemically active material is next mixed with a first portionof an alkaline electrolyte solution. The alkaline electrolyte solutionis preferably potassium hydroxide and is preferably added in an amountof about 40% of the total volume of the electrolyte to be added. Thisratio is, however, not critical as a 100% of the electrolyte can beapplied in the first step, providing the blending system or equipmentcan produce a lump free pumpable anode gel. It has been determinedhowever, that a preferable range for the first portion of theelectrolyte is between about 20% to about 60% of the total volume ofelectrolyte. A second indium compound is next added to the composition.The second indium compound may be either indium sulfate, indium oxide,indium hydroxide, or indium acetate and can be either in the form of asolution or a powder. Finally, this step is followed by the addition ofthe remainder of the alkaline electrolyte and a gelling agent. This laststep can include the addition of nucleation additives such as magnesiumoxide, magnesium hydroxide, calcium oxide, calcium hydroxide, zirconiumoxide and any combination thereof. The nucleation additives can also beadded directly to the electrochemically active material before any ofthe steps described herein. In all of the steps the electrochemicallyactive material is thoroughly mixed to ensure complete and homogenousmixing of each component added.

The steps described need not be carried out strictly in the sequentialorder described above. Some of the steps, for example, can be carriedout simultaneously with the proviso that anode composition results inrechargeable cell which provide better performance. For example, in oneembodiment, the addition of the first indium compound can be addedsimultaneously with the organic surfactant. The anode compositionprepared by the embodiments described herein need no further treatmentsuch as washing and drying before being assembled into the cells.

A gelled zinc anode manufactured by the method described herein can beused in rechargeable alkaline manganese dioxide/zinc galvanic cells.These cells can be assembled in cylindrical, button, coin or prismaticformats. Zinc anodes manufactured by the method of the present inventiontypically contain 1.43 to 2.4 grams of zinc powder per cm³ of gel.

In the case of rechargeable cells using pasted or flat electrodes,depending on whether the cell is assembled in the charged or dischargedstate, there can be a ratio of zinc to zinc oxide of from 10/90(discharged state) to 100/0 (fully charged state). The aqueouselectrolyte is usually 25% to 40% potassium hydroxide, optionally withzinc oxide dissolved in it up to saturation. The negative electrode isprocessed by kneading the zinc/zinc oxide powder mixture with 4% to 10%colloidal PTFE suspension by weight of zinc, and the paste issubsequently applied to at least one side of a current collector by e.g.a rolling process followed by an optional pressing step.

A variety of cathode materials can be used with the anode 18 of thepresent invention. The cathode active materials may comprise one ofmanganese dioxide, manganese oxyhydroxide, bismuth modified manganesedioxide, silver oxide, nickel oxyhydroxide or oxygen in an airelectrode. Electrolytic manganese dioxide is suitable for use in thepositive electrode with the zinc electrode of the present invention.Also included with the manganese dioxide is: 4% to 15% by weight ofgraphite and carbon black to provide conductivity; minor amounts below1% by weight of a hydrophobic lubricant such as polytetrafluoroethylene,polyethylene or a metal stearate to provide lubricity during processingand facilitate gas penetration into the electrode; the addition ofcompounds such as barium oxide, hydroxide or sulfate, in the range of 3to 15% by weight to improve performance during discharge/dischargecycling: and 0.01% to 10% finely divided hydrogen recombination catalystsuch as silver or its oxides or hydrogen absorbing alloys such asLaNi_(x) or NiTi_(y), to prevent pressure build-up from gassingresulting from corrosion of the zinc: and enough 20% to 40% potassiumhydroxide electrolyte solution to substantially fill the pores of themanganese dioxide and the pores between the solid powders of thecathode.

Various examples will now be described. The cells are AA size or IECLR6, but rechargeable. These have been subjected to various tests asidentified, but in all cases the default charge condition is 12 hoursvoltage-limited taper charge to an end voltage of 1.65 volts.

In each trial four cells were tested on each test. Some anode designswere evaluated in several trials as noted in the tables.

The subject of this disclosure is the anode preparation process. Thecritical requirements to evaluate the designs are electrical cyclingperformance and gassing. In the rechargeable alkaline manganese zinccell design, performance is measured using similar discharge loads andvoltage endpoints as primary alkaline manganese zinc cells.

In performance test 1, cells are deep-discharged through a 3.9-Ohmresistor load to 0.80V, then recharged as described above and furtherdischarged and recharged for a total of 25 cycles. This test representsmotor/toy applications. Performance in Ah-capacity is reported for thefirst discharge cycle and cumulative performance in Ah is reported overthe 25 cycles.

Performance test 2 is similar to performance test 1, except that thedischarge is through a 2.2-Ohm resistor load to 0.8V, representinghigher rate applications.

Gassing of rechargeable alkaline manganese zinc cells is necessarilyhigher than that of primary cells as a result of the recharging andlonger service life. It is desirable to keep internal cell pressurebelow 350 psi, which in the AA size cell design represents below about 9ml of in-cell gas in order to avoid leakage and provide a suitablefactor of safety with respect to cell hardware and the safety vent whichis not resealable. The following two tests have been found to be severeand are practical for predicting suitability for consumer use.

In gassing test 1, fresh cells are stored for 2 weeks at 65 C., thendeep discharged through 2.2 Ohms to 0.80V and recharged for a total of 5cycles, then stored for approximately one month at room temperature. Thecells are then punctured, the gas collected, measured and reported inml.

In gassing test 2, cycled cells are stored at high temperature. Cellsare first deep discharged through 2.2 or 3.9 Ohms to 0.80V and rechargedfor a total of 5 cycles, then stored for 1 week at 65 C., then deepdischarged and recharged for 5 more cycles, then stored forapproximately one month at room temperature. The cells are thenpunctured, the gas collected, measured and reported in ml.

In the examples given the design of the can, cathode, separator andelectrolyte remains the same and only the anode design and process ofpreparation is changed.

EXAMPLE 1

The zinc used in anode designs A through H is a powder of lead-free zinccontaining 133 ppm bismuth, with particle size distribution 19%+60 mesh,30% −60+100 mesh, 21%−100 +140 mesh, 20%−140+200 mesh, 9%−200+325 meshand 0.4%−325 mesh. Test result in table 1.

In design A the anode is prepared according to the prior art methoddescribed in U.S. Pat. No. 5,626,988. The zinc in the amount of 65% byweight of the anode is mixed with an aqueous solution of polyethyleneglycol surfactant of molecular weight 600 in the amount of 0.05% byweight of surfactant to the weight of the gelled anode. The zinc is thenmixed with an aqueous solution of indium sulfate in the amount of 0.1%indium by weight to the weight of zinc in the anode. A portion of theelectrolyte is then added and mixed. Carbopol gelling agent is thenadded in the amount 0.054% by weight to the weight of the anode andmixed. The remaining electrolyte is then added in an amount to provide atotal weight of electrolyte of 33% by weight to the weight of the anode.The performance and gassing results of the other designs in example 1are compared to the results of this control design and process.

In design B the anode constituents are the same as in design A. However,in anode design B, the order in which the constituents are mixed differfrom that in anode design A. In design B, a first portion of theelectrolyte is added and mixed first followed by the surfactant and thenthe indium sulfate solution. A second portion of the electrolyte is nextmixed together with the gelling agent. The first portion is typicallychosen at the 40% level of the total of first and second portion ofelectrolyte. This ratio is not critical for the purpose of thisinvention, as all the electrolyte could be applied as the first portion(100%), provided the blending system or equipment can produce a lumpfree pumpable anode gel. However, it was determined that a preferablerange for first electrolyte is between 20 and 60%, most preferably 40%,which was used for the examples of this application. The performance ofthis design is 1 to 9% higher than design A and the gassing is similaror less. The alkaline plating process created by adding electrolytebefore the surfactant and indium sulfate solution provides benefits.

In design C the anode constituents are the same as in design B, but thesurfactant is mixed with the zinc before the addition of any electrolyteand the indium sulfate solution is added after addition of the firstportion of electrolyte. The addition of indium sulphate is followed bythe addition of a second portion of the electrolyte and the gellingagent. The performance of this design is on average lower than designs Aand B, and gassing is somewhat higher as well, but still within anacceptable level of gas as required by the cell hardware. There does notappear to be any benefit in mixing the zinc with surfactant before theaddition of electrolyte.

Design D is similar to design B except that solid indium oxide powder isused in place of indium sulfate solution in an amount to provide 0.1%indium by weight to the weight of zinc in the anode. Performance of thisdesign is 6 to 13% higher than control group A and better than group Bas well. However, this benefit is offset by gassing that is up to fourtimes that of designs A and B, but is still within the acceptable levelof gas determined by the cell hardware.

Design E is similar to design D except that the amount of indium oxideused provided 0.2% indium by weight to the weight of zinc in the anode,double that of design B. Performance of this design is on average aboutthe same as design D and gassing is lower than design D but still higherthan designs A and B. In primary alkaline cells, amounts of indium of0.10% to zinc or higher are typically avoided as a gassing inhibitorbecause of undesirable effects on performance, but in this rechargeablealkaline cell design there is a demonstrated benefit in the higherlevels of indium, both for gassing and performance.

In design F, the anode constituents are the same as in design D, but thesurfactant is mixed with the zinc before the addition of any electrolyteand the indium oxide powder is mixed in after the addition of the firstportion of electrolyte. A second portion of the electrolyte is thenmixed together with the gelling agent. In this design, performance ismuch better than design A but there is no benefit to performance versusdesign D and gassing is slightly higher. Of these two process designs,mixing in the surfactant and indium oxide after the electrolyte isbetter.

Design G is similar to design B and D except that 0.02% of the totalindium is mixed in as indium sulfate solution after the first portion ofelectrolyte, and 0.08% of the total indium is mixed in as indium oxidepowder after the addition of the indium sulfate solution. Performance ismuch higher than design A, and similar to design D. Gassing is higherthan design A and similar to design D. The use of indium sulfatesolution to provide 0.02% of the indium does not seem to have thedesired effect of moderating the gassing.

Design H is similar to design G except that 0.05% of the total indium ismixed in as indium sulfate solution and 0.05% of the total indium asindium oxide powder. Performance is 1 to 6% higher than design A, but upto 6% lower than design D. Gassing is up to 3 times higher than design Aand about two thirds of design D. The use of indium sulfate solution toprovide one-half of the indium does have the desired effect ofmoderating the gassing, offset by a slight decrease in performance.

This example demonstrates the principle that rechargeable performancecan be increased and gassing controlled by means of anode designs andprocesses where the organic surfactant and indium compound inhibitors isadded after the zinc is mixed with electrolyte, or partly before andpartly after the zinc powder is mixed with electrolyte. It alsodemonstrates that the choice of indium compound and when it is addedduring the process is important with respect to performance enhancementand the management of gassing.

EXAMPLE 2

The zinc powder used in anode designs J through P is lead-free zinccontaining 133 ppm bismuth as in example 1, but of a much finer particlesize. The particle size distribution is 10% +60 mesh, 19%−60+100 mesh,18%−100+140 mesh, 18%−140+200 mesh, mesh and 19%−325 mesh. Test resultsappear in table 2.

Anode design J is prepared in the same manner as design A of example 1and serves as the prior art control design to which the other designs ofthis example are compared. It gives higher first discharge performancethan design A, but similar or lower cumulative performance over 25cycles. Gassing is a little higher than design A, but at a low level.

In design K, the surfactant and indium sulfate are mixed in after aportion of the electrolyte as in design B after which a second portionof the electrolyte together with the gelling agent is added and mixed.The alkaline plating process created by adding electrolyte before thesurfactant and indium sulfate solution provide little performancebenefit in this case but some benefit in reduced gassing.

Design L is prepared as in design D with surfactant and indium oxidepowder added after electrolyte. Similar to the results in design D,cumulative performance is greatly enhanced, in this case by 13% on test1 and 7% on test 2. Gassing is 1.5 to 2 times that of design J, but thisincrease is less than that of design D versus design A.

Design M is prepared in a similar way to design L, except that indiumhydroxide powder is used in place of indium oxide powder. Compared tocontrol design J, performance is similar or lower and gassing is similaror a little higher. Compared to design L with indium oxide, performanceis lower and gassing the same or lower. There seemed to be no advantageto mixing indium hydroxide with the zinc of this example.

In design N the surfactant is mixed with the zinc. Then, 0.02% of indiumto zinc is mixed into the zinc as indium sulfate solution. The zinc isthen mixed with a first portion of the electrolyte. 0.08% of indium tozinc is next added and mixed in as indium sulfate solution followed bythe remainder of the electrolyte and together with the gelling agent.Compared to design J where the surfactant and all of the indium sulfateis added before any electrolyte, performance is a little higher andgassing is a little lower. Compared to design K, where the surfactantand all of the indium sulfate solution is added after a portion of theelectrolyte, performance and gassing are similar.

Design P is prepared similarly to design N, except that 0.05% indium tozinc is added and mixed as indium sulfate solution before anyelectrolyte and 0.05% indium to zinc is added and mixed as indiumsulfate solution after a first portion of the electrolyte. Performanceis similar to that of the control design J and gassing is somewhatlower. Compared to design K, performance and gassing are similar.

This example demonstrates the performance improvement achieved by mixingthe indium compound, particularly indium sulfate after mixing in thezinc with a first portion of the electrolyte. It further demonstratesthe possibility of reducing gassing by mixing a first portion of indiumsulfate solution before any electrolyte and the second remaining portionof indium sulfate solution after mixing a first portion of theelectrolyte.

EXAMPLE 3

The zinc powder used in anode designs Q through V is zinc containing400–550 ppm lead. The particle size distribution is 22%+60 mesh,34%−60+100 mesh, 22%−100+140 16%−140+200 mesh, 6%−200+325 mesh. Testresults appear in table 3.

Anode design Q is prepared in the same manner as design A of example 1and serves as the prior art control design to which the other designs ofthis example are compared. It gives higher first discharge performancethan design A, but lower cumulative performance over 25 cycles. Gassingis at a low level.

In design R, the surfactant and indium sulfate are added and mixed aftera first portion of the electrolyte as in design B. This is then followedby the addition and mixing of a second portion of the electrolyte and agelling agent. The alkaline plating process created by the mixing in ofthe first portion of the electrolyte before the surfactant and indiumsulfate solution provide 10% and 3% benefits in cumulative performance.Gassing is increased up to double the low levels of the control designQ.

Design S is prepared as in design D with surfactant and indium oxidepowder added and mixed after a first portion of the electrolyte. This isthen followed by the mixing and addition of a second portion of theelectrolyte and a gelling agent. Similar to the results in design D,cumulative performance is greatly enhanced, in this case by 8% on test 1and 16% on test 2. Gassing is lower on test 1 but 3 times that of designQ on test 2.

Design T is prepared in a similar way to design M, using indiumhydroxide powder in place of indium oxide powder. Compared to thecontrol design Q, both first discharge and cumulative performance arehigher and gassing is lower in test 1 and 3 times higher in test 2.Compared to design S with indium oxide, performance is lower and gassingis similar. Contrary to design M of example 2 above, with this zincthere is a performance benefit in using indium hydroxide instead ofindium sulfate but not as much benefit as when using indium oxide.

In design U, the surfactant is mixed with the zinc powder. 0.02% ofindium to zinc is next mixed into the zinc as indium sulfate solution.The zinc is then mixed with a first portion of the electrolyte. 0.08% ofindium to zinc is then added and mixed as indium oxide powder followedby a second portion of the electrolyte and the gelling agent. Comparedto design Q, where the surfactant and all of the indium as indiumsulfate is added before any electrolyte, performance on first dischargeis similar and cumulative performance is 18% and 5% higher. However,gassing is about 3 times higher. Compared to design S where thesurfactant and all of the indium oxide powder is mixed in after a firstportion of the electrolyte, performance is not quite as high, butsurprisingly gassing with this zinc is 4 times higher on one test andsimilar on the other.

Design V is prepared similarly to design U, except that 0.05% indium tozinc is added and mixed in as indium sulfate solution before anyelectrolyte and 0.05% indium to zinc is mixed in as indium oxide powderafter a portion of the electrolyte. Cumulative performance is 13% higheron test 1 and similar on test 2 versus that of the control design Q andgassing is 2 to 3 times higher. Compared to design S, where thesurfactant and all of the indium oxide powder is added and mixed inafter a portion of the electrolyte, performance is not quite as high,but surprisingly gassing with this zinc is two and a half times higheron one test and similar on the other.

This example, carried out with leaded zinc alloy, further demonstratesthe benefit to performance of mixing to this zinc-lead alloy, surfactantand indium compound, particularly indium oxide and, indium hydroxideafter mixing the zinc-lead alloy with electrolyte. It furtherdemonstrates that gassing of the zinc can be managed by mixing part ofthe indium in an acid environment before adding electrolyte and mixingin the remaining indium in an alkaline environment after addingelectrolyte.

EXAMPLE 4

The zinc powder used in anode designs W through Z is zinc alloycontaining 104 ppm aluminum, 119 ppm bismuth, 200 ppm indium. Theparticle size distribution is 20%+60 mesh, 35%−60+100 mesh, 23%−100+140mesh, 17%−140+200 mesh, 6%−200+325.Test results appear in table 4. Asthe zinc alloy contains 200 ppm indium or 0.02%, the indium added in theanode preparation process is reduced to 0.08% to zinc to provide a totalof 0.10% indium to zinc by weight in the anode.

Anode design W is prepared in the same manner as design A of example 1and serves as the prior art control design to which the other designs ofthis example are compared. It gives similar first discharge performanceto design A, but much lower cumulative performance over 25 cycles.Gassing is at a low level, somewhat lower than that of design A.

In design X, the surfactant and indium sulfate are added and mixed inafter a portion of the electrolyte as in design B. The alkaline platingprocess created by mixing the electrolyte before the surfactant andindium sulfate solution provides a 7% benefit in cumulative performance.Gassing is similar to the low levels of the control design W.

In design Y, as in design N, the surfactant is mixed with the zincpowder. 0.016% of indium to zinc is next mixed into the zinc as indiumsulfate solution. The zinc is then mixed in with a first portion of theelectrolyte. 0.064% of indium to zinc is then mixed in as indium sulfatesolution. This step is followed by the addition and mixing of the secondportion of the electrolyte and the gelling agent. Compared to design W,where the surfactant and all of the indium sulfate is mixed in beforeany electrolyte, first discharge performance is 8% and 6% higher andcumulative performance is a little lower on one test and a little higheron the other. Gassing is higher but still at a low level. Compared todesign X where the surfactant and all of the indium sulfate solution ismixed in after a portion of the electrolyte, first discharge performanceis higher but cumulative performance is lower. Gassing is higher butstill at a low level. Similar to design U, in design Z the surfactant ismixed with the zinc. Then 0.016% of indium to zinc is mixed into thezinc as indium sulfate solution. The zinc is then mixed with a firstportion of the electrolyte. 0.064% of indium to zinc is next added andmixed in as indium oxide powder. This is then followed by the additionand mixing of the gelling agent and a second portion of the electrolyte.Compared to design W where the surfactant and all of the indium is mixedin as indium sulfate before any electrolyte, first discharge performanceis 3% and 9% higher and cumulative performance is 9% and 5% higher.Gassing is 4 times higher on test 1 but at a tolerable level, and loweron test 2. Compared to design Y where indium sulfate solution instead ofindium oxide is mixed in after the electrolyte, first dischargeperformance is lower on one test and similar on the other, butcumulative performance is 11% higher on one test and similar on theother. Gassing is higher on one test, lower on the other, but still at atolerable level.

This example demonstrates that even with zinc containing other metalssuch as aluminum, bismuth and indium, as corrosion inhibitors and forother purposes, a combination of choice of indium compounds and theorder of mixing in the anode composition process can be used to improvecell performance and manage zinc gassing.

EXAMPLE 5

This example uses the same zinc as in example 1, except that nucleationadditives are added during the process as well. The nucleation additivescan be added directly to the zinc before the first portion of theelectrolyte or with the gelling agent. In this example the nucleationadditive was added before the first electrolyte. Test results appear intable 5.

Anode design A of example 1 serves as the prior art control in thiscomparison. Also, design B and D of example 1 are listed for reference.The performance and gassing results of the other designs in example 5 iscompared to the results of the control design A.

Design BB is similar to design B except that 0.5% magnesium oxide byweight of anode is mixed in as nucleation agent during the anodepreparation process. Performance of this design over 25 cycles issimilar to 3% better than prior art control design A, but the gassing isonly half on gassing test 1 and lower on gassing test 2. Compared todesign B, the cumulative performance is about the same, but gassing islower.

Design BC is similar to design B and BB except that a higher amount of1% magnesium oxide by weight of anode is added and mixed in asnucleation agent during the anode preparation process. Performance of oninitial discharge is similar to 9% lower than design A, but over 25cycles cumulative this design showed already a 5 to 6% benefit and thegassing is much lower as well. Compared to design B, the cumulativeperformance is about the same, but gassing is lower.

Design DD is similar to design D except that 0.05% magnesium oxide byweight of anode is mixed in as nucleation agent during the anodepreparation process. Performance of this design over 25 cycles is 15 to23% better than prior art control design A, but the gassing is only halfon gassing test 1 and lower on gassing test 2. Compared to design D,performance is 2 to 15% better with much reduced gassing.

Design BE is similar to design B except that 0.05% calcium oxide byweight of anode is added and mixed in as nucleation agent during theanode preparation process. Performance of this design over 25 cycles issimilar to 11% better than prior art control design A and gassing islower. Compared to design B, performance is similar to 6% better withlower gassing levels.

Design DF is similar to design D except that 0.05% calcium oxide byweight of anode is added and mixed in as nucleation agent during theanode preparation process. Performance of this design over 25 cycles is12 to 15% better than prior art control design A, but gassing is higherthan design A. Compared to design D, performance is similar to 5% betterwith only half the gassing on gassing test 1 and somewhat lower gassingon test 2.

Design BG is similar to design B except that 0.05% calcium hydroxide byweight of anode is mixed in as nucleation agent during the anodepreparation process. Performance of this design over 25 cycles is 4 to8% better than prior art control design A and gassing is lower. Comparedto design B, performance is 3% better with somewhat lower gassinglevels.

Design BH is similar to design B and BG except that a higher amount of0.5% calcium hydroxide by weight of anode is mixed in as nucleationagent during the anode preparation process. Performance of this designover 25 cycles is similar to 11% better than prior art control design Aand gassing is lower. Compared to design B, performance is similar to 6%better with lower gassing levels.

This example demonstrates that the use of nucleation additives can beadvantageously applied in this anode process to improve cell performanceand manage zinc gassing.

The 5 examples together demonstrate in rechargeable alkaline manganesezinc cells a means of maximizing performance and managing gassing to atolerable and safe level with zinc powders containing various alloyingmetals and of various particle size distributions by a choice of indiumcompounds and the order in which surfactant and indium compounds aremixed in during manufacture of the anode composition, which manufacturerequires no subsequent washing, rinsing, drying or other steps beforebeing assembled into cells.

The polyethylene glycol surfactant used is soluble in water butinsoluble in the concentrated potassium hydroxide electrolyte. Indiumsulfate is soluble in water but only slightly soluble in theelectrolyte. Indium oxide and hydroxide are even less soluble thanindium sulfate. The most efficient and effective method of applyingthese organic and metallic corrosion inhibitors and mixing the zinc withsurfactant and then mixing with indium by cementation is by usingaqueous solutions of surfactant and indium sulfate to mix the zincbefore mixing of any alkaline electrolyte. Surprisingly, as demonstratedby the examples above, performance can be enhanced and gassing inrechargeable cells can still be managed to a suitable level by mixingpart or all of the inhibitors after mixing in of electrolyte.

TABLE 1 Lead-free zinc-bismuth alloy Performance Test 1 Performance Test2 Gassing Gassing No. Order of addition of Zn, PEG, Cycle 25 Cycle 25Test 1 Test 2 Anode of indium compound and Cycle % vs Cumulative % vsCycle % vs Cumulative % vs Average Average Design trials electrolyte(KOH) 1 Ah Control- Ah Control 1 Ah Control- Ah Control ml ml A 9 Zn,PEG, In2(SO4)3, KOH 1.57 18.97 1.24 15.40 1.8 2.5 [Prior Art] B 6 Zn,KOH, PEG, In2(SO4)3 1.58 1% 19.20 1% 1.35 9% 16.23 5% 1.9 2.0 C 1 Zn,PEG, KOH, In2(SO4)3 1.56 −1% 17.63 −7% 1.31 6% 15.14 −2% 3.4 1.9 D 4 Zn,KOH, PEG, In2O3 1.70 8% 21.49 13% 1.31 6% 16.60 8% 7.2 3.7 E 1 Zn, KOH,PEG, In2O3(0.2% 1.61 3% 20.56 8% 1.38 11% 17.56 14% 4.2 3.0 In to Zn) F1 Zn, PEG, KOH, In2O3 1.56 −1% 20.80 10% 1.34 8% 16.84 9% 7.9 5.5 G 1Zn, KOH, PEG, In2(SO4)3 (0.02% In to Zn), In2O3 (0.08% 1.59 1% 20.33 7%1.38 11% 16.78 9% 7.7 3.5 In to Zn) H 1 Zn, KOH, PEG, In2(SO4)3 (0.05%In to Zn), In2O3 (0.05% 1.59 1% 19.26 2% 1.31 6% 16.01 4% 5.2 2.4 In toZn

TABLE 2 Lead-free zinc-bismuth alloy, finer particle size PerformanceTest 1 Performance Test 2 Gassing Gassing No. Order of addition of Zn,PEG, Cycle 25 Cycle 25 Test 1 Test 2 Anode of indium compound and Cycle% vs Cumulative % vs Cycle % vs Cumulative % vs Average Average Designtrials electrolyte (KOH) 1 Ah Control- Ah Control 1 Ah Control- AhControl ml ml J 2 Zn, PEG, In2(SO4)3, KOH 1.63 17.38 1.34 15.40 2.3 3.2[Prior Art] K 1 Zn, KOH, PEG, In2(SO4)3 1.63 0% 17.82 3% 1.33 −1% 15.10−2% 2.6 1.8 L 3 Zn, KOH, PEG, In2O3 1.59 −2% 19.66 13% 1.33 −1% 16.55 7%4.6 4.8 M 2 Zn, KOH, PEG, In(OH)3 1.54 −6% 16.52 −5% 1.30 −3% 15.63 1%2.2 4.4 N 1 Zn, PEG, In2(SO4)3 (0.02% In 1.70 4% 17.82 3% 1.39 4% 15.03−2% 2.1 2.0 to Zn), KOH, In2(SO4)3 (0.08% In to Zn) P 1 Zn, PEG,In2(SO4)3 (0.05% In 1.61 −1% 17.87 3% 1.29 −4% 15.02 −2% 2.4 1.8 to Zn),KOH, In2(SO4)3 (0.05% In to Zn)

TABLE 3 Zinc-lead alloy Performance Test 1 Performance Test 2 GassingGassing No. Order of addition of Zn, PEG, Cycle 25 Cycle 25 Test 1 Test2 Anode of indium compound and Cycle % vs Cumulative % vs Cycle % vsCumulative % vs Average Average Design trials electrolyte (KOH) 1 AhControl- Ah Control 1 Ah Control- Ah Control ml ml Q 2 Zn, PEG,In2(SO4)3, KOH 1.60 16.75 1.34 14.94 2.9 1.1 [Prior Art] R 1 Zn, KOH,PEG, In2(SO4)3 1.59 −1% 18.44 10% 1.37 2% 15.33 3% 3.6 2.4 S 2 Zn, KOH,PEG, In2O3 1.72 8% 19.41 16% 1.42 6% 17.11 15% 2.1 3.4 T 2 Zn, KOH, PEG,In(OH)3 1.66 4% 17.96 7% 1.37 2% 16.15 8% 1.8 3.7 U 1 Zn, PEG, In2(SO4)3(0.02% 1.61 1% 19.71 18% 1.32 −1% 15.64 5% 7.9 3.6 In to Zn), KOH, In2O3(0.08% In to Zn) V 1 Zn, PEG, In2(SO4)3 (0.05% 1.58 −1% 19.01 13% 1.27−5% 15.01 0% 5.2 3.1 In to Zn), KOH, In2O3 (0.05% In to Zn)

TABLE 4 Zinc-aluminum-bismuth-indium alloy Performance Test 1Performance Test 2 Gassing Gassing No. Order of addition of Zn, PEG,Cycle 25 Cycle 25 Test 1 Test 2 Anode of indium compound and Cycle % vsCumulative % vs Cycle % vs Cumulative % vs Average Average Design trialselectrolyte (KOH) 1 Ah Control- Ah Control 1 Ah Control- Ah Control mlml W 1 Zn, PEG, In2(SO4)3, KOH 1.50 16.85 1.27 13.61 1.6 1.8 [Prior Art]X 1 Zn, KOH, PEG, In2(SO4)3 1.47 −2% 18.00 7% 1.29 2% 14.52 7% 1.8 1.9 Y1 Zn, PEG, In2(SO4)3 (0.016% In 1.62 8% 16.59 −2% 1.34 6% 14.27 5% 2.02.9 to Zn), KOH, In2(SO4)3 (0.064% In to Zn) Z 1 Zn, PEG, In2(SO4)3(0.016% 1.55 3% 18.41 9% 1.34 6% 14.45 6% 4.8 1.1 In to Zn), KOH, In2O3(0.064% In to Zn)

TABLE 5 Lead-free zinc-bismuth alloy w/nucleation agents as anodeadditive Performance Test 1 Performance Test 2 Gassing Gassing No. Orderof addition of Zn, PEG, Cycle 25 Cycle 25 Test 1 Test 2 Anode of indiumcompound and Cycle % vs Cumulative % vs Cycle % vs Cumulative % vsAverage Average Design trials electrolyte (KOH) 1 Ah Control- Ah Control1 Ah Control- Ah Control ml ml A 9 Zn, PEG, In2(SO4)3, KOH 1.57 18.971.24 15.40 1.8 2.5 [Prior Art] B 6 Zn, KOH, PEG, In2(SO4)3 1.58 1% 19.201% 1.35 9% 16.23 5% 1.9 2.0 D 4 Zn, KOH, PEG, In2O3 1.70 8% 21.49 13%1.31 6% 16.60 8% 7.2 3.7 BB 1 Zn, KOH, PEG, In(SO4)3, 1.58 1% 19.51 3%1.14 −8% 15.17 −1% 0.7 1.8 0.5% MgO BC 2 Zn, KOH, PEG, In(SO4)3, 1.43−9% 19.89 5% 1.24 0% 16.36 6% 1.1 0.6 1% MgO DD 1 Zn, KOH, PEG, In2O3,1.51 −4% 21.83 15% 1.36 10% 18.91 23% 0.9 1.6 0.05% MgO BE 1 Zn, KOH,PEG, In(SO4)3, 1.56 −1% 18.85 −1% 1.37 10% 17.08 11% 1.2 1.4 0.05% CaODF 1 Zn, KOH, PEG, In2O3, 1.69 8% 21.16 12% 1.40 13% 17.43 13% 3.3 3.60.05% CaO BG 1 Zn, KOH, PEG, In(SO4)3, 1.54 −2% 19.64 4% 1.33 7% 16.598% 1.2 2.0 0.05% Ca(OH)2 BH 1 Zn, KOH, PEG, In(SO4)3, 1.62 3% 19.40 2%1.38 11% 17.12 11% 1.5 1.9 0.5% Ca(OH)2

1. A rechargeable cell that performs at least twenty-five discharge andcharge cycles comprising: a cathode having an electrochemically activepowder including an oxide of manganese; an anode comprising an anodecomposition, said anode composition comprising an electrochemicallyactive zinc alloy powder, wherein said composition is manufactured by amethod comprising the step of mixing said zinc alloy with an alkalineelectrolyte solution, an organic surfactant, an indium compound, and agelling agent, such that said indium compound is added in an alkalineenvironment and wherein the organic surfactant is added after thealkaline electrolyte; a separator including at least one semipermeablemembrane; and an electrolyte solution in the separator, the cathode andthe anode, and filling pores thereof.
 2. The rechargeable cell of claim1, wherein said indium compound is comprised of a first indium compoundand a second indium compound.
 3. The rechargeable cell of claim 2,wherein said first and second indium compound is selected from the groupconsisting of indium sulfate solution, indium sulfate powder, indiumoxide solution, indium oxide powder, indium hydroxide solution, indiumhydroxide powder, indium acetate solution, and indium acetate powder andany combination thereof.
 4. The rechargeable cell of claim 2, whereinthe indium compound makes up from about 0.05 to about 0.5% by weight ofthe electrochemically active zinc.
 5. The rechargeable cell of claim 1,wherein said anode composition further comprises a nucleation additiveselected from the group consisting of magnesium oxide, magnesiumhydroxide, calcium oxide, calcium hydroxide, zirconium oxide, or anycombination thereof.
 6. The rechargeable cell of claim 5, wherein saidnucleation additive is present up to 2.5% by weight of the anode.
 7. Therechargeable cell of claim 1, wherein said electrochemically active zincmaterial comprises a metallic zinc or a zinc alloy.
 8. The rechargeablecell of claim 1, wherein said organic surfactant is present in the rangeof from about 0.1% to about 0.25% by weight of said electrochemicallyactive zinc material.
 9. The rechargeable cell of claim 1, wherein saidalkaline electrolyte comprises an aqueous solution of potassiumhydroxide having a concentration of about 5.5 molar to about 12 molar.10. The rechargeable cell of claim 9, wherein said electrolyte is addedin a first and second portion.
 11. The rechargeable cell of claim 10,wherein said first portion of said electrolyte is about 100% of totalvolume of electrolyte.
 12. The rechargeable cell of claim 10, whereinsaid first portion of said electrolyte is between about 20% and about60% of total electrolyte volume.
 13. The rechargeable cell of claim 12,wherein said first portion of said electrolyte is about 40% of totalvolume of said electrolyte.
 14. A rechargeable cell that performs atleast twenty-five discharge and charge cycles comprising: a cathodehaving an electrochemically active powder including an oxide ofmanganese; an anode comprising an anode composition, said anodecomposition comprising an electrochemically active zinc material,wherein said composition is manufactured by a method comprising thesteps of: mixing said zinc material with an organic surfactant; mixingsaid zinc material with a first indium compound; mixing said zincmaterial with a first portion of an alkaline electrolyte; mixing saidzinc material with a second indium compound; and mixing said zincmaterial with a second portion of said electrolyte and a gelling agent,wherein the organic surfactant is add after the alkaline electrolyte andwherein the first indium compound and the second indium compound areadded in an alkaline environment; a separator including at least onesemipermeable membrane; and an electrolyte solution in the separator,the cathode and the anode, and filling pores thereof.
 15. Therechargeable cell of claim 14, wherein said first and second indiumcompound is selected from the group consisting of indium sulfatesolution, indium sulfate powder, indium oxide solution, indium oxidepowder, indium hydroxide solution, indium hydroxide powder, indiumacetate solution, and indium acetate powder and any combination thereof.16. The rechargeable cell of claim 15, wherein said first and secondindium compound make up from about 0.05 to about 0.5% by weight of theelectrochemically active zinc.
 17. The rechargeable cell of claim 14,wherein said anode composition further comprises a nucleation additiveselected from the group consisting of magnesium oxide, magnesiumhydroxide, calcium oxide, calcium hydroxide, zirconium oxide, or anycombination thereof.
 18. The rechargeable cell of claim 17, wherein saidnucleation additive is present up to 2.5% by weight of the anode. 19.The rechargeable cell of claim 14, wherein said electrochemically activezinc material comprises a metallic zinc or a zinc alloy.
 20. Therechargeable cell of claim 14, wherein said organic surfactant ispresent in the range of from about 0.1% to about 0.25% by weight of saidelectrochemically active zinc material.
 21. The rechargeable cell ofclaim 14, wherein said alkaline electrolyte comprises an aqueoussolution of potassium hydroxide having a concentration of about 5.5molar to about 12 molar.
 22. The rechargeable cell of claim 21, whereinsaid first portion of said electrolyte is about 100% of total volume ofelectrolyte.
 23. The rechargeable cell of claim 21, wherein said firstportion of said electrolyte is between about 20% and about 60% of totalelectrolyte volume.
 24. The rechargeable cell of claim 23, wherein saidfirst portion of said electrolyte is about 40% of total volume of saidelectrolyte.